The present invention relates to a tank-type switchgear in which movable contact elements of main and auxiliary contacts are moved by driving means through a link mechanism.
In a conventional switchgear of this type, as shown in FIG. 1, a manhole 2 is often formed in the perimeter of a cylindrical tank 1 to make it possible to inspect a main contact 3 or an auxiliary contact 4 disposed in the tank 1. The size of the switchgear has been recently reduced. To reduce the diameter D of the tank and the distance L between the tanks, it is necessary to dispose the manhole 2 along the line B--B, which slants by a predetermined angle with respect to line A--A along which the tanks are aligned. In such a case, for ease of inspection, it is preferable to dispose the main and auxiliary contacts 3 and 4 within the tank 1 along line B--B along which the manholes 2 are arranged.
As shown in FIGS. 2 and 3, the main contact 3 comprises a stationary contact element 5 and a movable contact element 6, and the auxiliary contact 4 comprises a stationary contact element 7 and a movable contact element 8. The stationary contact elements 5 and 7 of the main and auxiliary contacts are electrically connected to a conductor 9 which is electrically insulated from and supported by the tank 1 through an insulated support member 10. The movable contact elements 6 and 8 of the main and auxiliary contacts 3 and 4 respectively oppose the stationary contact elements 5 and 7 and are connected to a link device 13. The link device 12 is disposed within a link box 12 supported by and electrically insulated from the tank 1 through an insulated cylinder 11. The link device 13 comprises an L-shaped main leve 15 rotatably connected to a stationary shaft 14 supported by the box 12, and an L-shaped auxiliary lever 17 rotatably connected to a stationary shaft 16 supported by the box 12. One end of the main lever 15 is connected to one end of the movable contact element 6 through a link 18 and connecting pins 19 and 20 at both ends thereof. One end of the auxiliary lever 17 is connected to one end of the movable contact element 8 through a link 21 and connecting pins 22 and 23 at both ends thereof. The other ends of the main and auxiliary levers 15 and 17 are connected to an insulated driving rod 29 extending into the insulated cylinder 11 through links 24 and 25 and connecting pins 26, 27 and 28. The driving rod 29 is connected to an unillustrated driving apparatus and transmits driving force from the driving apparatus to the link device 13.
In the conventional switchgear described above, as shown in FIG. 2, when the insulated driving rod 29 is driven downwards by the driving apparatus, the main and auxiliary levers 15 and 17 are respectively rotated in the counterclockwise direction around the stationary shafts 14 and 16. The movable contact elements 6 and 8 of the main and auxiliary contacts are then moved leftwards through the links 18 and 21, thereby opening the main and auxiliary contacts 3 and 4. On the other hand, when the driving rod 29 is moved upwards, the main and auxiliary levers 15 and 17 are rotated in the clockwise direction, and the movable contact elements 6 and 8 are moved rightwards, thereby closing the contacts 3 and 4.
In such a switchgear, to reduce the size of the tank 1, it is preferable to dispose the main contact 3 and the auxiliary contact 4 such that, as shown in FIG. 3, the center of a circle 30 enclosing the main and auxiliary contacts 3 and 4 and contacting the outer surfaces thereof is located approximately at the axis of the cylindrical tank 1. However, the link box 12 extends downwards to support the stationary shaft 16 which is a fulcrum of the auxiliary lever 17. Accordingly, the distance 1.sub.1 between the center of the circle 30 and the bottom end of the box 12 is large, increasing the size of the link box 12. Also, the distance between the tank 1 and the box 12 must be longer than a predetermined length to ensure electrical insulation therebetween. Accordingly, the conventional switchgear has the disadvantages that the inner diameter of the tank is large, increasing the size of the tank.